fix(dev-infra): exit non-zero if commit message validation failed (#36723)

Currently the `commit-message` validation script does not exit
with a non-zero exit code if the commit message validation failed.

This means that invalid commit messages are currently not
causing CI to be red. See: https://circleci.com/gh/angular/angular/686008

PR Close #36723

dev-infra/commit-message/validate-range.ts

@@ -39,7 +39,12 @@ export function validateCommitRange(range: string) {
     };
     return validateCommitMessage(m, options);
   });
+
   if (allCommitsInRangeValid) {
     console.info('√  All commit messages in range valid.');
+  } else {
+    // Exit with a non-zero exit code if invalid commit messages have
+    // been discovered.
+    process.exit(1);
   }
 }